Method of securing or positioning workpieces for machining operations



Dec. 29, 1970 P. e. DAVIS 3,550,245

METHOD OF SECURING OR POSITIONING WORKPIECES FOR MACHINING OPERATIONSFiled April 4, 1968 9 Sheets-Sheet 1 M2 KM f 457. @971 3,550,245 IECESDec. 29, 1970 P. G. DAVIS METHOD OF SECURING OR POSITIONING WORKP FORMACHINING OPERATIONS 9 Sheets-Sheet 2 Filed April 4, 1968 Hill Dec. 29,1970 P. 5.v DAVIS 3,550,245 METHOD OF SECURING OR POSITIONING WORKPIEGESFOR MACHINING OPERATIONS Filed April 4, 1968 9 sheets-sheets QWWA Dec.29, 1970 P. ca. DAVIS 3,550,245

METHOD OF SECURING 0R POSITIONING WORKPIECES FOR MACHINING OPERATIONSFiled April 4, 1968 9 Sheets-Sheet 4 I F%-/Z/ ff (5.9 w @8657 $5.9

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METHOD OF SECURING OR POSITIONING WORKPIE FOR MACHINING OPERATIONS FiledApril 4, 1968 9 Sheets-Sheet 5 ,lmnz;

Dec. 29, 1970 DAVIS 3,550,245

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Dec. 29, 1970 P. e. DAVIS 3,550,245

METHOD OF SECURING OR POSITIONING WORKPIECES FOR MACHINING OPERATIONSFiled April 4. 1968 9 Sheets-Sheet 8 I 7 Hm I l Q I I l f f/Z/J [J00 IZ65 I \W L- l I I l 1 /5 i x n r I I 1J1; 11 5" 111.)

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United States Patent 3,550,245 METHOD OF SECURING OR POSITIONING WORK-IIECES FOR MACHINING OPERATIONS Peter Grant Davis, London, England,assignor to The Molins Machine Company Limited, London, England, acorporation of Great Britain Filed Apr. 4, 1968, Ser. No. 718,750 Claimspriority, application Great Britain, Apr. 14, 1967, 17,248/ 67 Int. Cl.B2311 17/00 U.S. Cl. 29-407 7 Claims ABSTRACT OF THE DISCLOSURE Thisinvention concerns improvements in or relating to methods of machiningworkpieces and in or relating to devices for Securing workpieces formachining operations.

A workpiece can be machined whilst secured to a holder, such as apallet, for example in a numerically controlled machine tool havingautomatic devices to locate the holder accurately in the machine tool.With some components it is not possible to perform all the necessarymachining operations on the workpiece from which the component is to bemachined at one setting of the workpiece on the holder. It is thussometimes necessary to secure the workpiece to the holder in a firstpositional relationship for the performance of a first machiningoperation on the workpiece, and then to release the workpiece from andresecure it to the holder in a second positional relationship for theperformance of a second machining operation on the workpiece. Forexample, a workpiece requiring machining on two opposite faces may besecured to a pallet with one of the faces facing the pallet so that theother face is exposed and can be machined by a first machiningoperation, and the workpiece may then be released from the pallet andinverted before resecuring it so that the machined face then faces thepallet and said one face is exposed and can be machined by a secondmachining operation.

In many cases it is required that the pattern of machining on theworkpiece performed by the second machining operation should bear anaccurate positional relationship to the pattern of machining performedby the first machining operation. Where accurate location of theworkpiece in the machine tool is achieved by accurate location of theworkpiece holder, it is essential, in such cases, that the position ofthe workpiece relative to the holder for the second machining operationbears an accurate predetermined relationship to its position relative tothe holder for the first machining operation. In particular, Where theholder is automatically located in the machine tool and the latter isnumerically controlled, performance of the machining operations in thecorrect positions relative to the workpiece under automatic control isentirely dependent on the workpiece being correctly positioned relativeto the holder. This is especially a requirement in an automaticproduction system, such as is described in U.S. patent application Ser.No. 695,817 in which work- 3,550,245 Patented Dec. 29, 1970 pieces aretransported on pallets of a common form to a plurality of numericallycontrolled machine tools each having automatic devices to locate saidcommon form of pallet.

According to the present invention there is provided a method ofmachining a workpiece comprising the steps of securing a marking deviceto a workpiece holder, securing the workpiece to the holder in a firstpositional relationship and so that the marking device makes a mark onthe workpiece, performing a first machining operation on the workpiecewhile it is secured to the holder in said first positional relationship,releasing the workpiece from the holder, resecuring the workpiece to aholder so that the mark on the workpiece is located at a determinedposition relative to the holder whereby the workpiece is secured in asecond positional relationship which bears a predetermined relationshipto said first positional relationship and which is accurately achievedby use of the mark on the workpiece as a reference, and performing asecond machining operation on the workpiece while it is secured in saidsecond positional relationship.

The holder to which the workpiece is secured for the second machiningoperation may be the same holder as, or a dilferent holder but of thesame form as, that to which it was secured for the first machiningoperation.

The workpiece in said second positional relationship may be invertedrelative to its position in said first positional relationship, and aplurality of marking devices may be secured to the holder and arrangedto make on the workpiece, when the latter is in said first positionalrelationship, at least two marks nominally defining the axis about whichthe workpiece can be considered to be rotated through during suchinversion. The marking devices may be secured to said holder nominallyin predetermined positions and the method may include the step ofmeasuring the deviation between the actual and nominal positions of themarking devices, and taking account of the measured deviation when usingthe marks to secure the workpiece in said second positionalrelationship.

The invention further provides devices for securing a workpiece formachining operations comprising a workpiece holder, a marking device,means to secure said marking device to said holder, and means to securea workpiece to said holder in a first positional relationship so thatthe marking device makes a mark on the workpiece, and to secure theworkpiece to the holder in a second positional relationship which bearsa predetermined relationship to said first positional relationship andcan be achieved by use of said mark as a reference. There may beprovided a plurality of marking devices. The marking device may comprisea hard tip, such as a diamond tip, adapted to make a spot indent on theworkpiece.

Methods and devices in accordance with the present invention will now bedescribed by way of example with reference to the accompanying drawingsin which:

FIG. 1 is a plan view of a pallet having three support elements fixedthereto, and showing in broken line a workpiece,

FIGS. 2, 3 and 4 are plan views of parts of a pallet having supportelements, different from those shown in FIG. 1, fixed thereto,

FIG. 5 is a plan view of a template on a pallet, drawn to a differentscale from that of FIG. 1,

FIG. 6 is a section on the line VIVI of FIG. 1, drawn to a differentscale,

FIG. 7 is a section on the line VH-VII of FIG. 1, drawn to a differentscale,

FIG. 8 is a section on the line VIII-VIII of FIG. 1, drawn to adifferent scale,

FIG. 9 is a side elevation of a marking device, drawn to the same scaleas FIG. 8,

FIG. 9A is a section through a support element and pallet with a deviceas shown in, and drawn to the same scale as FIG. 9,

FIG. 10 is a side elevation of a further locating device, drawn to thesame scale as FIG. 9,

FIG. 11 is a section through a modified form of support element with anassociated fixing device, drawn to a different scale from that of FIG.9,

FIG. 12 is a view similar to FIG. 6, but drawn to a different scale, andshowing a different form of fixing device,

FIG. 13 is a view similar to FIG. 12 showing a further form of fixingdevice,

FIG. 14 is a plan view of a support element fixed to a pallet, drawn toa different scale from that of FIG. 1,

FIG. 15 is a section on the line XV-XV of FIG. 14, further showing aworkpiece,

FIG. 16 is a section through a pallet and a workpiece fixed thereto,drawn to a different scale from that of FIG. 1,

FIG. 17 is a plan "view of part of a pallet with a support element andassociated clamping member fixed thereto, drawn to a different scalefrom that of FIG. 1,

FIG. 18 is a section on the line XVIIIXVIIl of FIG. 17,

.FIG. 19 is a plan view of part of a pallet with a different supportelement and associated clamping member fixed thereto, drawn to the samescale as FIG. 17,

FIG. 20 is a section on the line XXXX of FIG. 19,

FIG. 21 is a plan view of part of a pallet with a further supportelement and associated clamping member fixed thereto, drawn to the samescale as FIG. 17,

FIG. 22 is a section on the line XXIIXXII of FIG. 21,

FIG. 23 is a plan view of a template on a pallet, drawn to a differentscale from FIGS. 17 to 22;

FIG. 24 is a side elevation of a template support, and

FIGS. 25 and 26 are sections through a pallet and support elements witha workpiece secured thereto, drawn to a different scale from that ofFIG. 1.

Referring to FIG. 1, a base member in the form of a pallet 1 hasprepared fixing locations consisting of tapped holes 2 arranged withtheir centers at the junctions of a square grid, the spacing of the holecenters, i.e. the distance between adjacent rows and between adjacentcolumns in the grid, being in the pallet shown 25 mm.

Further features of the pallet are side extensions or lugs 3, providedso that pairs of pallets can be linked together as described in U.S.patent application Ser. No. 695,817 a datum pad 4 at one corner,provided for locating a tool in a manner described in U.S. patentspecification Nos. Re. 25,956 and 3,241,451 and hole locations forsensing devices used in a manner described in U.S. patent specificationNo. 3,243,178 for automatic location of the pallet in a machine tool.

Support elements 6, 7 and 8 are mounted on the pallet 1. Each supportelement has at least one raised support surface for supporting aworkpiece and a plurality of prepared fixing positions, consisting ofholes through the support element, selected pairs of which can registerwith pairs of tapped holes 2 in the pallet 1. Thus the support element 6has a single raised circular support surface 9 and fixing holes 10, 11,12, 13, 14, 15, 16 and 17, of which holes 11 and 17 are shown inregistration with tapped holes 2 in the pallet 1.

The fixing holes -17 in the support element 6 are offset one fromanother in two directions at right angles, corresponding to thedirections of the rows and columns of the grid on which the tapped holes2 are arranged in the pallet 1. The spacing between the centers of thefixing holes in these directions is one half, or a multiple of one half,the spacing between the centers of the holes 2 in the pallet 1, whichlatter spacing is 25 mm. Thus, for example, the centers of holes 10 and11 are spaced by 12.5 mm., and the centers of holes 12 and are spaced by37.5 mm. In other words, the centers of the fixing holes 10-17 lie atthe junctions ,(but not with a hole at every junction) of a square gridhaving a spac- 4 ing (i.e. the distance between adjacent rows andbetween adjacent columns) of 12.5' mm., which is half the spacing of thegrid of the tapped holes 2. The center of the support surface 9 is alsopositioned at a junction of the grid of the fixing holes.

By this arrangement, the center of the support surface 9 can, byregistration of different selected pairs of fixing holes with pairs oftapped holes 2, be arranged at different positions relative to thepallet 1 and can, in fact, be located at any junction of a square gridhaving a spacing of 12.5 mm. In FIG. 1 the fixing holes 11 and 17 areshown in registration with tapped holes 2, but if, for example, thesupport element were moved to the right as viewed in FIG. 1 to registerthe fixing hole 10 with the tapped hole 2 with which hole 11 is shown inregistry, and to register the fixing hole 16 with the tapped hole 2 withwhich hole 17 is shown in registry, the support surface 9 would be moved12.5 mm. to the right from its position shown in FIG. 1.

The support element 7 has three raised circular sup port surfaces 18, 19and 20 for supporting a workpiece, and is provided with fixing holes 21,22, 23, 24, 25, 26, 27 and 28 of which holes 24 and are shown inregistration with tapped holes 2. The fixing holes in the element 7 are,like those in the element 6, so positioned that their centers lie atjunctions of a square grid having a spacing of 12.5 mm., and the supportsurfaces 18, 19 and 20 are also positioned with their centers atjunctions of the same grid. The positional relationship of the supportsurfaces to the support element 7 is fixed, but by registration ofselected pairs of fixing holes with selected tapped holes 2 the supportelement 7, and hence the support surfaces 18, 19 and 20 can be arrangedat different positions relative to the pallet 1.

The support element 8 has two raised circular support surfaces 29 and 30for supporting a workpiece, and is provided with fixing holes 31, 32,33, 34, 35, 36, 37, and 38 of which holes 31 and 38 are shown inregistration with tapped holes 2 in pallet 1. Again, the fixing holesare positioned with their centers at junctions of a square grid having aspacing of 12.5 mm., and the support surfaces 29 and 30 also have theircenters positioned at junctions of the same grid. The support surfaces29 and 30, whose positions relative to the support element 8 are fixed,can thus be arranged at different positions relative to the pallet 1 byregistration of selected pairs of fixing holes with selected tappedholes 2.

Further support elements 39, 40 and 41 are shown in FIGS. 2, 3 and 4respectively. The element 39 has two raised circular support surfaces 42and 43 and fixing holes 44, 45, 46, 47, 48, 49, 5t} and 51, of whichholes 47 and 48 are shown in registration with tapped holes 2 in thepallet 1. The element 40 has two raised circular support surfaces 52 and53, and fixing holes 54, 55, 56, 57, 58, 59, and 61 of which holes 56and 59 are shown in registration with tapped holes 2 in the pallet 1.The element 41 has four raised circular support surfaces 62, 63, 64 and65 and fixing holes 66, 67, 68, 69, 70, 71, 72, and 73 of which holes 69and 70 are shown in registration with tapped holes 2 in the pallet 1.The fixing holes in the support elements 39, 40 and 41 are like those inthe support elements 6, 7 and 8 previously described, arranged withtheir centers at junctions of a square grid having a spacing of 12.5mm., and the support surfaces have their centers at junctions of thesame grid. Thus each support element, and hence its support surfaces,can be arranged at different positional relationships to the pallet 1 byregistration of selected pairs of fixing holes with selected tappedholes 2.

By selection of one or more support elements from the elements 6, 7, 8,39, 40 and 41, and by registration of selected pairs of fixing holeswith selected tapped holes 2 in the pallet, a wide variety of supportarrangements for workpieces, i.e. of positional relationships of supportsurfaces to the pallet 1, can be achieved. A support sur face can bearranged at any junction of a square grid having a spacing of 12.5 mm.and therefore a part designer has considerable freedom since he can makea selection of such junctions (subject to avoidance of interferencebetween adjacent support elements) for supporting locations on theworkpiece from which the part is to be made. By this arrangement thetapped holes 2 in the pallet 1 can 'be relatively widely spaced (25 mm.)and a comparatively close spacing (12.5 mm.) of possible positions forthe center of a support surface can be achieved.

One of the many possible supporting arrangements is illustrated in FIG.1, which shows a workpiece 74 (in broken line) supported on the supportsurfaces 9, 18, 19, 20, 29 and 30. To facilitate the fitting of thesupport elements to the pallet .1 in the correct desired positions, atemplate 75, shown in FIG. 5, is provided. The template is somewhatlarger than the pallet and has apertures consisting of cut-out profiles7 6, 77 and 78 corresponding respectively to the profile sizes andshapes (as viewed in plan) of the support elements 6, 7 and 8 andarranged in the desired positional arrangement of the support elements.The template has a cut-back 79 at one corner, which corresponds to andlocates against the datum pad 4, and has different diameter holes 80 and81, adjacent diagonally opposed corners, which are provided to fit overcorresponding different diameter dowels arranged at a work setting tablewhere the workpiece is secured to the pallet, the latter being locatedat the work setting table in predetermined positional relationship tothe dowels. 'In this manner the template can be applied to, i.e. placedon, the pallet in a predetermined positional relationship thereto sothat the cut-outs 76, 77 and 78 lie over the pallet at the desiredpositions of the support elements. The template may also have printingon its top side, e.g. giving instructions regarding the tooling requiredfor the workpiece, so that a work setter knows that the template is thecorrect way up when the printed side is uppermost. When the template hasbeen applied to the pallet in the correct positional relationship thesupport elements 6, 7 and 8 can then be mounted on the pallet at thepositions defined by the cut-outs 76, 77 and 78, respectively, byplacing the support elements in the cut-outs.

It will be appreciated that a different template is provided for eachrequired support arrangement. It will be noted that each of the supportelements 6, 7 and 8 (FIG. 1) and 39, 40, 41 (FIGS. 2, 3 and 4respectiely) has a differently shaped profile, so that only a correctlyshaped support element can be fitted to the pallet in a position definedby a cut-out in a template, since a wrong support element would not fitthe cut-out. It will further be noted that the profile shapes of thesupport elements 6 and 7, having respectively one support surface (9)and three support surfaces (18, 19 and 20), are totally asymmetric, sothat there is only one possible orientation of the support element whichfits the cut-out in the template. However, the support elements 8, 39and 40, each of which has two support surfaces, have their profiles soshaped that they can fit a cut-out in a template in either of twoorientations, 180 displaced from each other, to achieve the samepositional relationship of support surfaces to the pallet. Thus, forexample, if the support element 8 were rotated through 180 from itsposition shown in FIG. 1, it would still fit the cut-out 78 (FIG. andthe positional relationship of support surfaces to the pallet would bethe same, but the support surface 29 would occupy the position in whichsupport surface 30 is shown, and vice-versa. The support element 41(FIG. 4), having four support surfaces, similarly has its profile shapedso that it can fit a correspondingly shaped cut-out in either of twoorientations, 180 displaced from each other, and retain the samepositional relationship of support surfaces to the pallet. By thisarrangement each template can have one or more cut-outs defining adesired selection and positional arrangement of support ele- 6 ments,which provides a unique positional relationship of support surfaces tothe pallet.

Referring now also to FIGS. 6, 7 and 8, the support elements are fixedto the pallet 1 by means of screws 82 which pass through the fixingholes and screw into the internal thread of the tapped holes 2 withwhich the fixing holes register. The support element is recessed aroundthe periphery of the upper end of each fixing hole to accommodate thescrew head, which has a recess 83, hexagonal in cross section, intowhich a key can be inserted to turn the screw.

FIGS. 6, 7 and 8 show the workpiece 74 in full line, and the template 75in broken line since, as is explained later, the template is in practiceremoved from the pallet before the workpiece is fixed to the supportelements. These figures also clearly show how the support surface (e.g.20 in FIG. 6) is raised from the rest of the support element to supportthe workpiece clear thereof and clear of the pallet .1.

Each of the support elements 6, 7, 8, 39, 40 and 41 has a hollow portionbeneath each support surface, the hollow communicating with a hole inthe support surface. Thus as can be seen for example in FIG. 6, there isa hole 84 through the support element extending from the support surfaceto the bottom face of the support element. The lower portion of the hole84 is of greater diameter than the upper portion, so that the supportelement has an internal circular shoulder 85. The hollow or hole 84 canaccommodate any one of a number of fixing or locating devices for theworkpiece.

FIG. 6 shows fitted in the hole 84 a fixing device comprising a member86 having an upper part 87 with an external screw thread and an internalrecess or keyway 88 of hexagonal cross section, and a lower flangedportion 89 which can abut against the shoulder 85. A spring 90 pushesagainst the base of the member 86 to urge it upwardly so that the part87 projects from the support surface 20, the lowermost coil of thespring being of larger diameter than the rest and adapted to fit in acircular recess 91 provided in the support element near the bottom ofthe hole 84 to hold the spring captive in the hole 84. Upward movementof the member 86 is limited by abutment of the flange 89 against theshoulder 85. This fixing device is used to secure the workpiece 74 tothe support surface 20 as follows.

The member 86, with its associated spring 90, is inserted into thehollow 84 from the bottom thereof (as viewed in FIG. 6) before thesupport element 7 is fixed to the pallet 1, the externally threaded part87 being caused to project from the surface 20 by the action of thespring 90. After the support element 7 has been fixed to the pallet 1,the workpiece 74, which has an internally threaded hole 92 at thelocation where it is to be fixed to the support surface 20, is placed onthe surface 20, thereby depressing the part 87 into the support elementagainst the action of the spring A key is then inserted, through thehole 92 in the work piece, into the recess 88 to turn the member 86 sothat the part 87 is threaded up into the hole 92, assisted by the actionof the spring 90. It will be appreciated that this form of fixing deviceleaves the upper surface of the workpiece clear and unobstructed byscrew heads or the like, and further perrnits the device to be screwedinto the workpiece when the side of the support element, i.e. its baseas viewed in FIG. 6, through which the device was inserted isinaccessible because it lies against the pallet 1.

FIG. 7 shows fitted in the hollow or hole 84, communicating with thesupport surface 30, a locating device 93 having a lower portion 94 ofincreased diameter, corresponding to the larger diameter of the lowerportion of hole 84, which provides a flange to abut against the shoulder85, and an upper portion 95, consisting of a plain dowel, which projectsfrom the support surface 30 to fit in a hole 96 in the workpiece 74 tocorrectly locate the latter. The lower portion 94 of the device 93 isslotted to accommodate a diametrical key member 97 which tightly fits ina keyway 98 (see FIG. 1) in the support element 8 to retain the locatingdevice in the support element and to prevent rotation of the locatingdevice 93.

FIG. 8 shows fitted in the hollow or hole 84, communicating with thesupport surface 9, a fixing device 99 having a lower portion 100 likethe lower portion 94 of the device 93 described above, of increaseddiameter to fit the larger diameter lower portion of hole 84 and toprovide a flange which can abut against the shoulder 85. The upperportion of the device 99 (whose position corresponds to that of thecentral portion of the device 93) is hollow and internally threaded sothat the workpiece 74 can be fixed to the support surface 9 by means ofa screw 101 passing through a hole 102 in the workpiece and threadedinto the device 99, the screw having a recess 103, of hexagonal crosssection, for a key in its head. The lower portion 100 of the device 99has (like the lower portion 94 of the device 93) a slot in which adiametrical key member 97, fitting in a keyway 98 in the supportelement, is accommodated to retain and prevent rotation of the device99.

In FIG. 9 there is shown a marking device 104 adapted to fit in a hollowor hole 84 in a support element. The main part of the device 104 isidentical to the fixing device 99 (FIG. 8), and therefore needs nofurther description, but screwed into the internal thread of the device104 is an externally threaded element 105 having a diamond tip 106. FIG.9A shows the device 104 fitted in the support element 8 (in place of thedevice 93 shown in FIG. 7) so that the diamond tip 106 projects from thesupport surface 30, and when a workpiece 74A is positioned and presseddown on to that support surface the diamond 106 indents the workpieceand provides a spot datum mark on the surface of the workpiece, whichmark can be used when the workpiece is later reset. Thus, for example,if a workpiece has to be reset, i.e. relocated in relation to a pallet,between two separate machining operations, the second of which isdependent on the first in that the required positioning of the workpiecefor the second operation depends on its positioning for the firstoperation, a device as shown in FIG. 9 can be used to mark the workpiecewhile it is supported for the first operation, and the mark can thenserve as a datum point for re-setting the workpiece in the correctposition for the second operation.

A particular use of the marking devices 104 occurs when it is requiredto machine a workpiece on opposite faces thereof. This may be achievedby securing the workpiece to a pallet with one of the faces facing thepallet and thereby inaccessible for machining) and subjecting theworkpiece to a first machining operation on the other of the faces,which is facing away from the pallet and is therefore exposed formachining. The workpiece is then released from the pallet and invertedbefore being resecured thereto so that the other face of the workpiece,which has been machined, faces the pallet and the one face of theworkpiece faces away from the pallet and can be machined by a secondmachining operation.

It will be appreciated that if the positional relationship of theworkpiece to the pallet for the second machining operation is the sameas that for the first machining operation, except for inversion of theworkpiece, the workpiece can be considered merely to have been rotatedthrough 180 about an axis through the workpiece, and parallel andbearing a fixed relationship to the surface of the pallet, during itschange from the first to the second positional relationship. Theworkpiece can then accurately be repositioned relative to the palletafter inversion by accurately relocating the axis about which theworkpiece is considered to have been rotated, and the position of theworkpiece along that axis, so that they bear the same relationship tothe pallet as when the workpiece was in the first positionalrelationship. Such accurate relocation of the workpiece is normallyrequired because it is usually necessary that the pattern of machiningon the workpiece effected by the second machining operation bears anaccurate predetermined positional relationship to the pattern ofmachining effected by the first machining operation.

The above can be achieved by securing a plurality of marking devices104, in support elements to the pallet 1 at positions such that when theworkpiece is secured to the pallet in the first positional relationshipat least two spot indent marks are made on the under surface of theworkpiece to define the axis about which the workpiece is considered tobe rotated to effect the required inversion, and the position of theworkpiece therealong. The marks are thus made to lie on a line parallelto the axis and in a plane containing said axis and normal to the palletsurface. When, after the first machining operation, the workpiece isreleased from the pallet and inverted, it can be accurately relocatedrelative to the pallet by positioning the workpiece to locate the marks,which are then on the upper surface of the workpiece, at the samepositions as previously over the pallet, i.e. the same positionsrelative to the pallet when the latter is viewed in plan.

In practice the marking devices 104 are secured, in Support elements, tothe pallet 1 nominally at the positions necessary to define the axis onthe workpiece, i.e. nominally at positions at junctions of the squaregrid on which the marking devices can be located, but there willnormally be a small unavoidable error between the actual and nominalpositions. When the workpiece is released from the pallet the actualpositions of the diamond tips 106 relative to the pallet are thereforeascertained by viewing the pallet, in plan, through a microscope and thedeviation between the nominal and actual positions is measured. Theworkpiece is then inverted and repositioned on the pallet by locatingthe marks, viewed through the microscope, at positions which account forthe measured deviations, in fact positions determined by applying amirror-image correction for the measured deviations. Conveniently themicroscope is provided with a visible digital read-out.

Normally the workpiece is resecured to the same pallet as that to whichit was secured for the first machining operation, but, if desired, theworkpiece may be resecured to a different pallet from, but of the sameform as, that to which it was secured for the first machining operation.For example, a different arrangement of support devices may be requiredto support the workpiece for the second machining operation, and it maybe more convenient to transfer the workpiece from one pallet to another,which is preloaded with the required different arrangement of supportdevices, rather than to change the arrangement of support devices on thepallet to which the workpiece was secured for the first machiningoperation.

It is to be understood that the particular manner of use of markingdevices 104 described above is given by way of example. The markingdevices can provide marks on a workpiece defining the positionalrelationship in which it was secured to the pallet, and can therefore beused in various ways to relocate the workpiece on the same, or anothersimilar, pallet in a position bearing an accurate predeterminedrelationship to said positional relationship.

In FIG. 10 there is shown a locating device 107 essentially similar tothe device 93 (FIG. 7) previously described, but having an upper portion108 terminating in a cone 109 having a fiat tip. When the device isfitted in a hollow or hole 84 of a support element so that the upperportion projects from a support surface into a hole in a workpiece, thetip of the cone 109 can act as a datum point for location by microscope.

The provision of a common form of hollow or hole 84 communicating witheach support surface in each of the support elements 6, 7, 8, 39, 40 and41, and of a plurality of different fixing and locating devices 86, 93,99, 107 and 105 adapted to fit in the hollow or hole 84 enablesdifferent fixing or locating requirements to be met by insertion ofappropriate fixing or locating devices in the appropriate hollows orholes communicating with the support surfaces at which the particularforms of fixing or locating are required.

The devices so far described are used as follows. When a particularworkpiece is to be machined, the support elements required forsupporting the workpiece are selected, as well as a template appropriatefor the required supporting arrangement, and the necessary fixing andlocating devices. For convenience and by way of example, the method ofsecuring the workpiece 74 to the pallet 1 in a manner as shown in FIG. 1will be described. In this case tlhe support elements 6, 7 and 8 areselected, as well as the template 75 (FIG. 5), three fixing devices 86(FIG. 6) for fitting in the support element 7, two locating devices 93(FIG. 7) for fitting in the support element 8, and one fixing device 99(FIG. 8) for fitting in the support element 6. There are also providedsix screws 82, for fixing the support elements to the pallet, and ascrew 101 for securing the workpiece to the support element 6. Theworkpiece 74 is prepared with threaded holes 92 (FIG. 6) at thepositions where it is to be secured to the support element 7, and plainholes 96 and 102 (FIGS. 7 and 8) at the positions where it is to belocated on and secured to the support elements 8 and 6 respectively.

The appropriate fixing or locating devices are fitted in the holes orhollows 84 in the support elements, i.e. the fixing devices 86 arefitted in the support element 7, the lower coil of the spring 90 beingpressed into the recess 91 to retain the device in the support element,the locating devices 93 are inserted in the support element 8 and thefixing device 99 is inserted in the support element 6, the devices 93and 99 being retained in their respective support elements by the keymembers 97.

The template 75 is applied to, i.e. laid on, the pallet 1 in apositional relationship thereto determined by location of the cut-back79 against the datum pad 4 on the pallet and registry of the holes 80and 81 over dowels provided at the work-setting table in fixedpositional relationship to the pallet. Printing on the upper side of thetemplate may provide a further check that the template is the correctway up. The support elements 6, 7 and 8 are then placed on the pallet inthe positions defined by the template, i.e. so that the support elements6, 7 and 8 respectively fit into the cut-outs 76, 77 and 78, and arefixed to the pallet by means of screws 82 passing through the fixingholes 11 and 17, 24 and 25, and 31 and 38 and threaded into the tappedholes 2 in the pallet with which these fixing holes register. Thetemplate 75 is then lifted vertically to remove it from the pallet.

The workpiece is placed on the support elements so that the preparedholes in the workpiece register with the holes 84 in the supportsurfaces, the projecting upper dowel portions 95 of the devices 93 inthe support element 8 locating in the holes 96 in the workpiece as shownin FIG. 7. The projecting threaded portions 87 of the devices 86 in thesupport element 7 are pressed down, against the action of the springs90, as the workpiece 74 is placed on the support surfaces 18, 19 and andare then screwed upwardly, assisted by the action of the springs, intothe threaded holes 92 in the workpiece by means of a key inserted in therecess 88, such upward movement being limited by engagement of theflange 89 against the shoulder 85 (see FIG. 6). The workpiece is securedto the support element 6 by threading the screw 101 through the hole 102in the workpiece into the internally threaded portion of the fixingdevice 99 (see FIG. 8).

It will be understood that the above described selection of supportelements and fixing and locating devices is 10 given only by way ofillustration and example and that a wide variety of support elements,fixing and locating devices for use in the support elements, andpositional relationships of the support elements to the pallet ispossible.

In FIG. 11 there is shown a modified form of support element 110 havinga hole or hollow 111, with a circular recess 112 and a shoulder 113, inwhich there is accommodated a fixing device 114, with associated spring115, which is identical to the fixing device 86 with spring (FIG. 6)previously described. The support element does not have a raised supportsurface, as does, for ex ample, the support element 7, but instead thereis provided a hollow part 116 whose upper portion has an internal threadcorresponding to the external thread on the upper portion of the fixingdevice 114, and an external thread of greater diameter, the part 116being adapted to rest on the support element 110. The purpose of thisarrangement is to enable a functional hole, in a workpiece i.e. a holehaving a function in the part to be pro duced from the workpiece, to beutilized for securing the workpiece during a machining operation. Thefunctional hole may have an internal thread and be of different diameterfrom the externally threaded upper portion of the fixing device 114. Thepart 116 can be provided with an external thread corresponding to thatof the functional hole in the workpiece. In practice, the part 116 isfirst threaded into the functional hole in the workpiece which is thenplaced over the support element 110 so that the part 116 is located overthe fixing device 114, depressing the latter against the action of thespring 115. The device 114 can then be screwed upwardly into theinternal thread of the part 116 by means of a key fitting in the recessin the upper portion of the device 114.

In FIG. 12 there is shown a support element 117, fixed to the pallet 1by a screw 82, and having a raised support surface 118 for supporting aworkpiece 119. The support element 117 has a hole 120, communicatingwith the support surface 118, and having a lower part 121 of increaseddiameter thus providing a shoulder 122. Fitted in the hole is a fixingdevice comprising a member 123 having an upper portion 124, with anexternal screw thread and an internal recess 125 of hexagonalcross-section, and a lower flanged portion 126 which fits in theincreased diameter part of the hole 121 and can abut against theshoulder 122. A spring 127 is coiled round a cylindrical core 128 fixedto a base disc 129 which fits in a recess in the flanged portion 126.The core 128 extends into a central hollow in the'rnember 123 which isprovided with an internal shoulder 130 against which the spring 127abuts. The fixing device can be used as follows. The workpiece 119,having an internally threaded hole 131 at the position where it is to besecured to the support surface 118, is placed on the support surface sothat the holes 131 and 120 register, thereby depressing the member 123against the action of the spring 127, the member 123 being shown in thedepressed position in FIG. 12. A key is then inserted, through the hole131 in the workpiece, into the recess 125 to thread the portion 124upwardly into the hole 131, such upward movement of the member 123 beingassisted by the action of the spring 127 pressing against the shoulder130, and being limited by abutment of the flanged portion 126 againstthe shoulder 122.

FIG. 13 shows the same support element 117 as FIG. 12 but with adifferent form of fixing device. The fixing device of FIG. 13 comprisesa member 132 essentially similar to the member 123 but with a centralhollow of the same diameter throughout its length (i.e. without theshoulder 130) in which a spring 133 is housed. A piston head 134, on arod 135 having a base disc 136, is also housed in the central hollow,abutting against the spring 133, the lower end the hollow having smallwelds 137 to retain the piston head in the hollow. The fixing deviceshown in FIG. 13 can be used in exactly the same way as that in FIG. 12,and in FIG. 13 the device is 11 shown with the member 132 in its raisedposition, i.e. with the externally threaded upper portion projectingfrom the support surface 118.

It will be seen that the fixing devices shown in FIGS. 6, 12 and 13 workon the same principle and all have the advantage that they can beinserted into a support element from one side thereof, when that side isaccessible, and can be screwed into a workpiece when the said one sideof the support element is inaccessible. The devices in FIGS. 12 and 13are not provided with means to retain them in support element but canreadily be so retained by holding against the base discs 129 and 136respectively.

As previously described, the pallet 1 with tapped holes 2 arranged atthe junctions of a square grid with a spacing of mm. and the supportelements 6, 7, 8, 39, and 41 (or similar support elements and 117- FIGS.11, 12 and 13) having fixing holes and support surfaces arranged withtheir centers at junctions of a square grid with a spacing of 12.5 mm.,enable support surfaces to be arranged at any of the junctions of asquare grid having a spacing of 12.5 mm. (subject to avoidance ofinterference between adjacent support elements) so that differentworkpieces can be supported providing the supporting locations on eachworkpiece lie at junctions of a square grid of 12.5 mm. spacing. Theoccasion may arise, however, where a workpiece which can be supported atone or more locations lying on that grid i.e. at locations on theworkpiece at which support surfaces can be arranged, requires additionalsupport at a further location not on that grid.

In FIGS. 14 and 15 there is shown fixed to the pallet 1 an adjustablesupport element 138 having a raised circular support surface 139, and alongitudinal slot 140. A rider 141 is slidably mounted in the slot andhas a hole to accommodate a screw 82 (as previously described) whichthreads into a tapped hole 2 in the pallet 1, the top of the rider beingrecessed to accommodate the screw head. By this arrangement the supportsurface 139 can be arranged at any position, within a range determinedby the extent of the slot 140, about a particular tapped hole 2 in thepallet. Thus the orientation of the support element can be selected byrotating it about the tapped hole 2 to which it is to be fixed, and thedistance of the support surface 139 from the tapped hole 2 can beselected by sliding the support element relatively to the rider 141.When the support surface is in the desired position the support elementcan be fixed to the pallet by threading the screw 82, through the holein the rider, into the tapped hole 2. By way of i lustration I theelement 138 is shown in two positions in FIG. 14, in one of which theelement is drawn in broken line. The support element 138 can, of course,be fixed to any of the tapped holes 2 in the pallet 1 and the supportsurface 139 can therefore be arranged at any position on the pallet.

In FIG. 15 the support element 138 is shown with a fixing device 99 (aspreviously described with reference to FIG. 8) fitted in the holecommunicating with the support surface 139. The device 99 has aninternal thread into which is screwed a screw 142, having a recess 143in its head, and which passes through a hole 144 in a workpiece 145, thehole 144 being of larger diameter at its upper part to accommodate thescrew head so that it does not project from the upper surface of theworkpiece. It will be appreciated that different selected fixing andlocating devices can be fitted in the support element 138 to meetdifferent fixing and locating requirements.

FIG. 16 shows a section through a pallet 146 having fixing locationsarranged at the junctions of a square grid or matrix with a spacing of25 mm. (as are the tapped holes 2 in the pallet 1 shown in FIG. 1) andwherein a fixing device 147, essentially similar to the fixing device 86previously described with reference to FIG. 6, is provided at eachfixing location. Thus, each fixing device 1.47 comprises a member withan externally threaded upper portion 148 with an internal recess 149 ofhexagonal cross section, and a lower flanged portion 150 against which aspring 151 presses. The fixing device is fitted in a hollow housing 152having a shoulder 153, against which the flange 150 can abut, and havinga circular recess 154 in which the lowermost coil of the spring can beaccommodated to retain the spring captive in the housing. The spring 151urges the member 147 upwardly to cause the upper externally threadedportion 148 to project from the top surface of the pallet. Each housinghas an upper, externally threaded portion 155 which projects slightlyfrom the upper surface of the pallet 146. A plurality of capping members156, each having an internal thread corresponding to the external threadon the housings, are provided to screw on to the housing and therebyretain the members 147 against the action of the springs 151 to cap andlimit projection of the externally threaded portions 148 from the topsurface of the pallet.

These capping members 156 are applied to the housings 152 at all fixinglocations other than those elected fixing locations at which the members147 are required to project from the pallet for fixing a workpiecethereto. It will be appreciated that by leaving different selections offixing locations uncapped, different numbers and positional arrangementsof projecting fixing devices 147 can be achieved and thereforeworkpieces requiring different fixing arrangements, i.e. requiringfixing at different positional relationships to the pallet, can beaccommodated.

At those selected fixing locations where a workpiece is to be fixed tothe pallet, i.e. the fixing locations at which a capping member 156 isnot screwed on to the housing 152, such as the central fixing locationshown in FIG. 16, a support element 157 having a raised support surface158 is screwed on to the housing in place of a capping member. Thesupport surface 158 has a central hole through which the externallythreaded upper portion 148 of the member 147 can project, urged upwardlyby the spring 151. A workpiece 159, having an internally threaded hole160 at the position where it is to be fixed, can then be fixed to thesupport element 157 and pallet 146 in a manner previously described,namely by placing the workpiece on the support element, with the hole160 in register with the hole in the support surface 158, therebydepressing the member 147 against the action of the spring 151, and theexternally threaded portion 148 can then be screwed up into the hole 160by the application of a key through the hole 160 into the keyway orrecess 149.

FIGS. 17 to 22 show support elements and associated clamping members forsecuring workpieces to the pallet 1.

Referring to FIGS. 17 and 18, a support element 161, having two raisedrectangular support surface 162 and 163, is provided with a fixing hole164 and a slot 165 arcuate about the fixing hole. The fixing hole 164can register with any of the tapped holes 2 in the pallet 1 and the meanradius of the slot 165 corresponds to the spacing of the square grid onwhich the tapped holes 2 lie (i.e. 25 mm.) so that the slot registerswith an adjacent tapped hole 2, the slot extending along an arc of 90 toensure that at least one tapped hole 2 registers with it whatever theorientation of the support element 161. The support surfaces 162 and 163can thus be arranged at different positional relationships to the pallet1 by registration of the fixing hole 164 with different tapped holes 2and by rotating the element 161 about the fixing hole 164 to achieve adesired orientation.

A workpiece can be supported on the support surfaces 162 and 163, andFIGS. 12 and 13 show (in broken line in FIG. 12 and full line in FIG.13) a finished part 166 machined from a workpiece so supported. Theworkpiece is secured to the support surfaces 162 and 163 by means of aclamping member 167 having two downwardly depending rectangular clampingsurfaces 168 and 169 which are positioned on the workpiece directlyabove the support surfaces 162 and 163. The profile of the clampingmember (as viewed in plan) is rectangular and corresponds to the profileof that part of the support element carrying the support surfaces for apurpose explained later.

The clamping member 167 is fixed to the pallet 1 by a screw 170 passingthrough a hole 171 in the clamp ing member, a registering hole 172 inthe workpiece, and the fixing hole 164 in the support element, andthreaded into the tapped hole 2 in the pallet 1 with which the fixinghole 164 registers. The support element 161 is further fixed to thepallet 1 by a screw 173 passing through the slot 165 and threaded into atapped hole 2 in registry with the slot.

A workpiece clamped and supported in this manner can, for example, bemachined to the shape of the part 166 shown in FIG. 17 and can haveholes 174 and 175 drilled therein.

FIGS. 17 and 18 show a workpiece supported on and clamped to bothsupport surfaces 162 and 163. It might be desired, however, to clamp aworkpiece to only one of the support surfaces, for example the surface162, in which case a packing piece, of the same thickness (i.e. height)as the workpiece, would be provided between the support surface 163 andthe clamping surface 169. The support surfaces 162 and 163 are providedwith holes or recesses 176 to accommodate projections from such apacking piece and thereby prevent it from slipping.

FIGS. 19 and 20 show fixed to the pallet 1 a support element 177 ofcircular shape ,(as viewed in plan), apart from a wedge-shaped cut-out178, and having four raised arcuate support surfaces 179, 180, 181 and182. The surfaces support a workpiece from which a part 183, shown inbroken line in FIG. 19 and full line in FIG. 20, is machined. Theworkpiece is secured to the support surfaces by means of a cross shapedclamping member 184 having four downwardly depending clamping surfaces,two of which, 185 and 186, are indicated in FIG. 20, which arepositioned on the workpiece directly above the support surfaces 179,180, 181 and 182. The clamping member and support element are fixed tothe pallet 1 in the same manner as previously described with referenceto the support element 161 and clamping member 167, namely by means of ascrew 170 passing through a central hole 187 in the clamping memher, alarge hole 188 in the workpiece, and a central fixing hole 189 in thesupport element, and threaded into a tapped hole 2, the support elementbeing further fixed to the pallet by a screw 173 passing through anarcuate slot 190 in the support element and threaded into an adjacenttapped hole 2. The profile (as viewed in plan) of the clamping member184 between adjacent clamping surfaces corresponds to the cut-out 178 inthe support element for a purpose explained later. A workpiece clampedin the manner shown in FIGS. 19 and 20 can, for example, be machined tothe shape of the part 183 and have four holes 191 drilled therein.

FIGS. 21 and 22 show fixed to the pallet 1 a support element 192,essentially similar to the support element 177, but having three raisedarcuate support surfaces 193, 194 and 195. Thus the element 192 is ofcircular shape (as viewed in plan) apart from a wedge-shaped cut-out 196(of different size from the cut-out 178). The support surfaces support aworkpiece from which a part 197 (shown in broken line in FIG. 21 andfull line in FIG. 22) is machined. A Y shaped clamping member 198 havingthree downwardly depending clamping surf-aces, two of which, 199 and200, are indicated in FIG. 22, is provided to clamp the workpiece to thesupport surfaces with the clamping surfaces directly thereabove. A screw170 passing through a central hole 201 in the clamping member, a largehole 202 in the workpiece and a central fixing hole 203 in the supportelement, and threaded into a tapped hole 2 in the pallet 1, and a screw173 passing through an arcuate slot 204 in the support element andthreaded into an adjacent tapped hole 2, fix the support element andclamping member to the pallet 1, as previously described. The profile(as viewed in plan) of the clamping member 198 between adjacent clampingsurfaces corresponds to the cut-out 196 in the support element for apurpose explained later. A workpiece clamped in the manner shown inFIGS. 21 and 22 can, for example, be machined to the shape of the part197 and have three holes 205 drilled therein.

It will be appreciated that the support elements shown in FIGS. 17 to 22can be fixed at different positions to the pallet 1 by registration oftheir fixing holes with different tapped holes 2, and can be fixed atdifferent orientations by reason of their arcuate slots extending round90 so that the slot registers with an adjacent tapped hole 2 whateverthe orientation of the support element. It is further to be understoodthat the support elements and associated clamping members described aregiven only by way of example and that other configurations of supportelements and support surfaces (and corresponding clamping members andclamping surfaces) may be provided. In particular, there may be providedfurther support elements, essentially similar to the element 161 (FIGS.17 and 18), but with different spacings between the support surfaces 162and 163, and other support elements, essentially similar to the elements177 and 192, but in which the support surfaces lie at different radii,together with corresponding clamping members.

To facilitate fixing of support elements and clamping members in desiredpositional relationships to the pallet 1, templates are provided, therebeing a separate template for each separate desired positionalarrangement of support elements. By way of illustration, FIG. 23 shows atemplate 206 having three apertures consisting of cutout profiles 207,208 and 209 corresponding respectively to the profile sizes and shapes(as viewed in plan) of the support elements 161, 177 and 192. Thetemplate 206, like the template (FIG. 5) previously described, has acut-back 210 at one corner, which locates against the datum pad 4 on thepallet 1, and two different diameter holes 211 and 212 located adjacentadjacent diagonally opposed corners, and is somewhat larger than thepallet 1. The template may further have printing on its upper surface.The holes 211 and 212 can locate over dowels to which the pallet 1 canbe positioned in predetermined relationship.

In use, the template 206 is applied to the pallet 1, which has beenpositioned relative to the dowels, by locating the holes 211 and 212over the dowels, and the template is thus laid on the pallet 1 inpredetermined positional relationship thereto. The support elements 161,177 and 192 are then placed on the pallet in positions definedrespectively by the cut-outs 207, 208 and 209, by placing the supportelements in the cut-outs, and screws 173 are placed through the arcuateslots in the support elements and threaded into the tapped hole 2 (or,in the case of the element 177 as shown in FIG. 19, one of the tappedholes 2) with which the slot registers. The template 206 is then liftedvertically and removed from the pallet. A workpiece, having preparedholes 172, 188 and 202 at locations corresponding to the positions ofthe support elements, is placed on the support surfaces, and thetemplate 206 is then placed on the workpiece in the same positionalrelationship to the pallet (determined by the dowels over which theholes 211 and 212 locate) as previously. The clamping members 167, 184and 198 are then placed on the workpiece at positions definedrespectively by the cut-outs 207, 208 and 209 by placing the clampingmembers in the cutouts. As described previously, part of the profile ofeach of the clamping members corresponds to part of the profile of theassociated support element, and hence to part of the profile of theappropriate cut-out in the template. Therefore, by locating the saidpart of the profile of the clamping member against the said part of theprofile of the cut-out in the template it can be ensured that theclamping surfaces are positioned on the workpiece directly above thesupport surfaces (which latter are, of course, obscured from view by theworkpiece). The clamping members are then fixed to the pallet by meansof screws 170 as previously described, and the template is removedvertically. In FIGS. 18, 20 and 22 the template is shown, in brokenline, in two positions, one on the pallet and the other on theworkpiece.

The preceding paragraph is intended merely to illustrate the generalmanner in which support elements and clamping members such as thoseshown in FIGS. 17 to 22 are used and applied. In practice, these supportelements and clamping members would normally be used together withfurther support elements and fixing or locating devices for theworkpiece as previously described with reference to FIGS. 1 to 16.

For example, the part 197 shown in FIGS. 21 and 22 might be made by aprocedure as follows. The support element 192 and a number ofsurrounding support elements with fixing devices like the supportelement 7 (FIG. 1) are fixed to the pallet 1 at positions defined by anappropriate template, the support element 192 being fixed only by ascrew 173 through the slot 204. After removing the template from thepallet, a workpiece which is blank, apart from holes for the fixingdevices, is fixed to the said surrounding support elements. Theworkpiece is then machined to cut the large hole 202 in it. Aftermachining, the template is placed on the workpiece, and the clampingmember 198 is applied to the workpiece at the position defined by theappropriate cut-out in the template, and fixed to the pallet by a screw170. The workpiece is then again machined to cut out the shape of thepart 197 and drill the holes 205. The workpiece, and the clamping memberand support elements can then be removed from the pallet. In some casesthe said surrounding support elements may be removed from the palletafter the clamping member is fixed and before the second machiningoperation.

FIG. 24 shows a template support mounted on a work setting table 213.The support comprises a holder 214 having two horizontal extensions 215spaced apart by the width of a template and adapted to underlie the sideedges of the template to support the latter in a horizontal position.The holder has a spring urged clip 216, beneath which is a stop 217A, sothat a template 217 can he slid along and between the extensions 215 andunder the clip 216 until it abuts against the stop 217A, to position andhold the template is predetermined relationship a to the holder.Attached to the holder are two sets of four peripherally concavedrollers 218 which run along two vertical guide rails 219 fixed to thetable 213 (one extension 215, guide rail 219, and set of rollers 218being obscured as viewed in FIG. 24), The holder 214 is fixed to acarrier 220 on an endless cord 221 passing round pulleys 222 mounted onfixed brackets 223 between the guide rails 219. The cord 221 furthercarries a counterweight 224 so that the holder 214, and a template heldtherein, will stay in a raised position by balance between thecounterweight and the weight of the holder and template. I

The working setting table 213 has a raised surface in front (i.e. to theleft as viewed in FIG. 24) of the guide rails 219 and is provided withupstanding rollers 225 which are rotatable about a vertical axis and arepositioned to fit T slots along the underside of the pallet 1 to whichthe template 217 is to be applied. The pallet 1 can thus be moved intopredetermined positional relationship to the guide rails 219 by runningthe T slots past the rollers 225 until the pallet abuts a stop (notshown), and the template 217 can be lowered onto the pallet inpredetermined positional relationship thereto, and raised verticallytherefrom by running the holder 24 down and up the guide rails 219,

The apparatus shown in FIG. 24 can thus be used to apply templates topallets for purposes previously described, and can replace the provisionof different diameter holes adjacent diagonally opposed corners of atemplate, and correspondingly positioned and sized dowels at the worksetting table, as described previously with reference to FIGS. 5 and 23.

FIGS. 25 and 26 show a modified form of the fixing device 86, shown inFIG. 6, particularly adapted for use when a workpiece is to be subjectedto a first machining operation whilst it is secured to a pallet, and isthen to be released from the pallet and inverted before being resecuredthereto for a second machining operation, and it is required that thepositional relationship of the workpiece to the pallet for the secondmachining operation bears a predetermined relationship to its positionalrelationship to the pallet for the first machining operation.

FIGS. 25 and 26 show two support elements 231 and 232, generally similarto, and fixed to the pallet 1 in the same manner as, those previouslydescribed. Each of the support elemets 231 and 232 houses a fixingdevice, essentially similar to the device 86 (FIG. 6) previouslydescribed, but having an accurate dowel portion 233 below an externallythreaded part 234, the upper end of the dowel portion 233 being adaptedto project from the raised support surface of the support element, asshown in FIGS. 25 and 26', when the lower flanged portion of the deviceabuts the shoulder provided in the support element.

The fixing devices shown in FIGS. 25 and 26 can be used as follows. Thesupports 231 and 232, containing the fixing devices, are secured to thepallet 1 at selected positions. Collars 235, adapted to fit over thedowel portions 233, are placed on the raised support surfaces of thesupport elements, and a workpiece 236, having pretapped holes 237 at aspacing corresponding to that between the two fixing devices, is placedon the collars so that the holes 237 register with the fixing devices.The workpiece is then secured to the support elements by screwing uponthe externally threaded parts 234 of the fixing devices into the tappedholes 237 in a manner as previously described with reference to FIG. 6,the parts 234 each having a recess into which a key can be inserted toeffect rotation thereof.

The positions of the support elements 231 and 232 on the pallet 1 areselected so that the axis of each dowel portion 233 intersects the axisof inversion about which the workpiece can be considered to be rotatedthrough during its inversion between a first and a second machiningoperation (as explained previously in relation to the marking deviceshown in FIGS. 9 and 9A). The tapped holes 237 in the workpiece arelocated so that their axes nominally also intersect this axis ofinversion.

The workpiece, thus secured to the pallet, is then subjected to a firstmachining operation which is made to include counterboring the upper (asviewed in FIG. 25) ends of the tapped holes 237 to produce circularrecesses 238 of accurate diameter corresponding to that of the dowelportions 233 and accurately positioned so that the axes of thecounterbores 238 intersect said axis of inversion. In other words, themachining operation, which is performed in accurate positionalrelationship to the pallet 1, is caused to produce counterbores 238directly over the dowel portions 233, which are themselves accuratelypositioned relative to the pallet.

After the first machining operation the workpiece 236 is released fromthe support elements, by unscrewing the fixing devices from the tappedholes 237, 'and inverted. The workpiece is then placed back on thesupport elements (after removal of the collars 235) and positioned sothat each tapped hole 237 registers with the same fixing device aspreviously. The fixing devices are screwed up into the tapped holes 237so that the dowel portions 233 are received, as shown in FIG. 26, in thecounterbores 238. In this way the workpiece is accurately located in the1 7 same positional relationship to the pallet as that which it occupiedfor the first machining operation, except for its inversion, and can besubjected to a second machining operation whose pattern of machining onthe workpiece bears a predetermined positional relationship to thepattern of the first machining operation. The requirement for accuratedowels and counterbores arises from the fact that sufficiently accuratepositioning may not be reliably achieved merely by use of screw partsthreaded into pretapped holes in the workpiece. In particular, there maybe errors in the positional relationship and accuracy of the tappedholes 237 in the workpiece since these holes are preformed before theworkpiece is secured to the pallet, i.e. independently of the actualmachining operations. By machining the counterbores 238 during the firstmachining operation, for example where the machining operation isperformed under numerical control the control tape or the like isprogrammed to include such counterboring, it can be ensured that thecounterbores 238 are made in the workpiece at positions bearing anaccurate predetermined relationship to the pattern of machining. Thus,by using these counterbores to effect relocation of the workpiecerelative to the pallet for the second machining operation, the workpiececan be positioned so that the pattern of machining performed by thefirst machining operation is accurately relocated relative to thepallet. The tapped holes 237 in the workpiece are intentionally arrangedto provide a relatively loose fit with the threaded parts 234, so thataccurate repositioning of the workpiece by fitting the counterbores 238over the dowels 233 can occur within the limits of such loose fit.

It will be noted that the workpiece is further spaced, by the height ofthe collars 235, from the pallet for the first machining operation thanfor the second machining operation, and the machining operations aretherefore performed in a manner which allows for this.

It is to be appreciated that the arrangement shown in FIGS. 25 and 26 isdescribed by way of illustration. In practice, the workpiece may besecured to the pallet 1 by further support elements and fixing orclamping devices, additional to those shown.

The method of relocating a workpiece described above with reference toFIGS. 25 and 26 may not provide the extreme accuracy achievable by useof diamond tipped marking devices in the manner explained previouslywith reference to FIGS. 9 and 9A. Notably, the method illustrated byFIGS. 25 and 26 depends on accurate location of the dowel portions 233relative to the pallet 1, and there may be some slight error in thislocation, i.e. the centers of the dowels may not lie exactly at thejunctions of the square grid on which they can nominally be located.However, the method illustrated by FIGS. 25 and 26 avoids the need foruse of microscopes to effect relocation of the workpiece and cantherefore be performed relatively quickly and and simply. This method isthus suited to workpieces which, although requiring relocation withconsiderable accuracy, do not need the extremely high degree of accuracyprovided by the method described with reference to FIGS. 9 and 9A, andwhich can advantageously be relocated on a pallet more quickly but witha lower degree of accuracy.

The devices described above can be used to particular adavntage in aproduction system for producing a variety of components which uses aplurality of pallets of a common form, in particular a plurality ofpallets like the described pallet 1, on which workpieces are transportedand delivered to a number of numerically controlled machine tools eachadapted to receive and automatically to locate such a pallet, forexample a production system as described in US. patent application Ser.No. 695,817.

What I claim as my invention and desire to secure by Letters Patent is:

1. A method of machining a workpiece comprising the steps of securing atleast one marking device to a work piece holder, securing the workpieceto the holder in a first positional relationship so that the markingdevice makes a mark on the workpiece, performing a first machiningoperation on the workpiece while it is secured to the holder in saidfirst positional relationship, releasing the workpiece from the holder,resecuring the workpiece to a holder so that the mark on the workpieceis located at a predetermined position relative to the holder wherebythe workpiece is secured in a second positional relationship which bearsa predetermined relationship to said first positional relationship andwhich is accurately achieved by use of the mark on the workpiece as areference, and performing a second machining operation on the workpiecewhile it is secured in said second positional relationship.

2. A method as claimed in claim 1 wherein the holder to which theworkpiece is secured for said second machining operation is the sameholder as that to which it was secured for said first machiningoperation.

3. A method as claimed in claim 1 wherein the holder to which theworkpiece is secured for said second machining operation is a differentholder from, but of the same form as that to which the workpiece wassecured for said first machining operation.

4. A method as claimed in claim 1 wherein the marking device is securedto said holder nominally in a predetermined position, and comprising theadditional steps of measuring the actual position of the marking deviceand correlating the measured position with the mark on the workpiecewhen securing the workpiece for said second machining operation.

5. A method as claimed in claim 4 comprising the step of securing aplurality of marking devices to the holder to which the workpiece issecured for said first machining operation so that a plurality of marksis made on the workpiece, and said marks serving as references forsecuring the workpiece in said second positional relationship.

6. A method as claimed in claim 5 wherein the work piece in said secondpositional relationship is inverted relative to its position in saidfirst positional relationship, and said marking devices are arranged tomake at least two marks on the workpiece nominally defining the axisabout which the workpiece can be considered to be rotated through duringsuch inversion.

7. A method as claimed in claim 6 where in the marklng devices aresecured to said holder nominally in predetermined positions to providemarks nominally defining said axis and comprising the additional stepsof measuring the deviation between the actual and nominal positions ofthe marking devices, and securing the workpiece in said secondpositional relationship by positioning the workpiece so that each marklies at a position determined in accordance with the measured deviation.

References Cited UNITED STATES PATENTS 2,901,934 9/1959 Dunham 81-533,229,365 1/1966 Fisher et al. 29-559 3,243,178 3/1966 Williamson et al.269-68 JOHN F. CAMPBELL, Primary Examiner V. A. DI PALMA, AssistantExaminer US. Cl. X.R. 29-559; 269-290

